Diabetes is a disease characterized by high levels of glucose in the blood. It results from defects in the action or secretion of insulin, a hormone secreted by the pancreas that promotes glucose uptake by the tissues, where it is used for energy.

Type 1 diabetes, which usually is diagnosed in children, results from destruction of the insulin-secreting cells of the pancreas. Patients are taught to give themselves insulin, through shots or other means, to keep their glucose levels in check.

Type 2 diabetes, formerly called adult-onset diabetes or noninsulin-dependent diabetes, is the most common form of the disease. It usually develops later in life and occurs when the tissues do not respond (become resistant) to insulin.

Symptoms of diabetes can include excessive thirst, frequent urination, hunger, fatigue, unexplained weight loss, sores that heal slowly, dry and itchy skin, tingling or loss of feeling in the feet and blurry eyesight.

For more information, visit the National Diabetes Education Program at www.ndep.nih.gov.

Complications of diabetes

A: Kidney disease

Diabetes can damage the glomeruli, the blood-filtering units of the kidneys (shown here). As a result, protein (green) is lost in the urine, and the kidneys gradually lose their ability to remove waste products (blue) from the bloodstream. Ultimately, the kidneys may fail and patients will require artificial kidney dialysis.

B: Heart disease

Most adults with diabetes have high blood pressure and high blood levels of triglycerides and low-density lipoprotein (LDL) cholesterol. Elevated cholesterol can lead to atherosclerosis, the build-up of fatty deposits in artery walls (shown here). Both high blood pressure and atherosclerosis, if untreated, can lead to heart attack or stroke.

C: Retinopathy

Diabetes can damage tiny blood vessels in the retina at the back of the eyeball. The damaged vessels can leak fluid into the retina, blurring vision. Fragile new blood vessels also may grow into the retina and leak blood (shown here) ultimately destroying the retina and causing blindness.

D: Nerve damage

Diabetes can damage nerves throughout the body, causing numbness. Sores may appear on numb areas of the foot because pressure or injury goes unnoticed. Poor circulation (shown here) may inhibit healing. If the injury is not treated and infection spreads to the bone, the foot may have to be amputated.